1. Field of the Invention
The invention relates to a process for the preparation of N,o-substituted mono- and/or polyurethanes of formula EQU R.sup.1 [--NHCOOR.sup.2 ].sub.n,
in which
R.sup.1 is an aliphatic, cycloaliphatic, aromatic, araliphatic, or heterocyclic radical, which may be substituted, PA0 R.sup.2 is an aliphatic, cycloaliphatic, or araliphatic radical which may be substituted with alkoxy or polyoxyalkylene groups, and PA0 n is a whole number from 1 to 5.
More particularly, the invention relates to a process for the preparation of N,o-substituted mono- and/or polyurethanes through the reaction of N-substituted allophanates and/or polyallophanates with alcohols R.sup.2 OH in the presence or absence of catalysts at temperatures of at least 160.degree. C., preferably from 165.degree. to 250.degree. C.
2. Prior Art
Industrially, urethanes are generally produced by the reaction of isocyanates with alcohols or of chloroformates with amines, whereby both the isocyanates and the chloroformates are obtained through the phosgenation of the corresponding amines and cleaving off hydrogen chloride or by the phosgenation of the alcohols (Methoden de organischen Chemie, Houben-Weyl, vol. 8, pp. 137, 120, and 101, Stuttgart: Georg Thieme Verlag, 1952). These processes are very expensive from a commercial standpoint; in addition, the use of phosgene results in significant disadvantages relating to the necessary safety and environmental measures.
Recently, a series of processes for producing urethanes has been described in which carboxylic acid derivatives are reacted with primary amines in the presence of alcohols.
In European Patent Application No. 18 581 (Canadian Pat. No. 1,121,373), aryl-mono- and/or -polyurethanes are prepared by reacting o-alkylcarbamates with primary aromatic mono- and/or polyamines in the presence of alcohols and, in some cases, urea. In German Application No. 31 22 013, N,N'-diarylureas are cited as the carboxylic acid derivatives, and in German Application No. 30 35 354, dialkylcarbonates are cited as the carboxylic acid derivatives.
In addition, Methoden der organischen Chemie, Houben-Weyl, vol. 8, mentions the alcoholysis of unsubstituted allophanates of formula H.sub.2 N--CO--NH--CO--OR to form N-unsubstituted carbamates (p. 206). No industrial teachings are given on the preparation of N-substituted urethanes.
German Application No. 31 08 067 describes a process for the preparation of N,o-disubstituted urethanes by reacting primary amines and alcohols with allophanates or mixtures of allophanates, urea, and/or carbamates, said mixtures possessing allophanates, at temperature of from 130.degree. to 350.degree. C. The presence of amines is absolutely necessary for the reaction to take place. This is also demonstrated by the examples.